Can't run sha256 more than once in intel sgx enclave

Question

So I'm trying to create two sha256 hashes in intel sgx using their cyrpto library. Currently, if I run the following:

sgx_sha256_hash_t *hash1;
int first = 1;
sgx_status_t = stat;
stat = sgx_sha256_msg( ( uint8_t * ) &first, 8, hash1 );

I have no problems, and I properly get hash1, however if I try

sgx_sha256_hash_t *hash1;
sgx_sha256_hash_t *hash2;
int first = 1;
int second = 2;
sgx_status_t = stat;
stat = sgx_sha256_msg( ( uint8_t * ) &first, 8, hash1 );
stat = sgx_sha256_msg( ( uint8_t * ) &second, 8, hash2 );

I get a segmentation fault. I tried doing this with the sha init, update, get_hash and close method instead, but with no imporved results, does anyone know why this might be? I was thinking I might be running out of memory in the enclave, if that's true, is there a way to expand my enclave?

Answer 1

You are writing your hashes to a random location in memory through those two uninitialised pointers, hence the segfaults. Also, your src_len parameters are incorrect, and for completeness the first parameter should be const.

So, what you want is:

sgx_sha256_hash_t hash1;    // note: no asterisk
sgx_sha256_hash_t hash2;
int first = 1;
int second = 2;
sgx_status_t = stat;
stat = sgx_sha256_msg( ( const uint8_t * ) &first, sizeof (first), &hash1 );
stat = sgx_sha256_msg( ( const uint8_t * ) &second, sizeof (second), &hash2 );